Kinetics and Mechanism of Radical‐Chain Oxidation of 1,2‐Substituted Ethylene and 1,4‐Substituted Butadiene‐1,3

The kinetic results of the radical chain oxidation of methyl linoleate (LH) in micelles were given. The oxidation rate depends on the average number of substrate molecules in the micelle and is almost independent of the micelle concentration under the given conditions. The chain propagation and termination were assumed to predominantly occur inside the micelle. Possible reasons for linear chain termination during the oxidation of polyunsaturated fatty esters in microheterogeneous systems were discussed.

Effect of microheterogeneity on the kinetics of oxidation of methyl linoleate in micelles

The process of lipid peroxidation (LPO) plays an extremely important role in the human body due to the fact that its uncontrolled development can lead to oxidative stress and a number of serious diseases. The traditional approach to the analysis of the mechanism and kinetics of LPO is based on the well-known ideas that emerged from the study of radical-chain oxidation of hydrocarbons in a homogeneous medium. However, the distinctive feature of LPO is that this process is heterogeneous and the processes of diffusion of active intermediates between the aqueous and hydrocarbon phases should play a significant role in it. In the present work, an attempt has been made to theoretically estimate the contribution of these processes to the oxidation kinetics of model substances used in practice in the study of LPO. In the course of the calculations, a quantum chemical and kinetic analysis of the role of hydroperoxyl radical in the radical-chain mechanism of oxidation of methyl linoleate in micelles was carried out. The molecular dynamics method shows the important role of changing the dynamic rigidity of a hydrocarbon fragment of a chain during the formation of a peroxyl radical and hydroperoxyl group during the oxidation of a substrate in a heterogeneous medium. Quantum chemical calculations of the thermodynamics of reactions involving $${{{\text{HO}}_{2}}^{ \cdot }}$$
 radicals and the effects of their solvation made it possible to estimate the kinetic constants of the reaction rates. Using kinetic modeling, their relative contribution to the oxidation kinetics was revealed. In this case, it is possible to explain a number of anomalies associated with the oxidation of polyunsaturated fatty acids and their esters in micelles compared with their oxidation in a homogeneous hydrocarbon medium.

Quantum chemical evaluation of the role of $${{{\text{HO}}_{2}}^{ \cdot }}$$ HO 2 · radicals in the kinetics of the methyl linoleate oxidation in micelles

The kinetics of chain initiation during the auto-oxidation of some unsaturated compounds (methyl linoleate, allyl acetate, allyl propyl ether, styrene, α-methyl styrene, butyl acrylate, butyl methacrylate, ethyl cinnamate, trans-1,2-diphenylethylene, trans,trans-1,4-diphenylbutadiene-1,3) in solvents of different polarity was studied at temperatures 343–383 K. The data array comprised of chain initiation rate constants of bi- and trimolecular reactions was obtained. It was shown that in some cases, the polarity of the medium is the key factor defining the initiation mechanism.

Kinetic features of chain initiation reactions during the oxidation of unsaturated compounds in media of different polarity

The kinetics of oxygen absorption during the oxidation of methyl linoleate in Triton X-100 micelles has been studied The order of the reaction with respect to the initiator diminishes from 1 to 06 with an increase in the total content of Triton X-100 per the unit volume of solution, since by the time of reaching the maximum oxygen absorption rate, the system consists of mixed micelles, which intercept the radicals generated by the initiator The results of the analysis can be used to assess the dynamics of solubilization of hydrophobic substrates for creating a technique to test the antioxidant activity of biologically important compounds

Features of Methyl Linoleate Oxidation in Triton X-100 Micellar Buffer Solutions

The results of experiments and computer simulations on the radical-chain oxidation of methyl linoleate in micelles are reported. The reaction rate constants included in the developed mathematical model are estimated. The ratio of the rates of first-order and bimolecular chain termination is examined. It is demonstrated that the rate constant of bimolecular chain termination in micelles is lower than that in the homogeneous phase.

Kinetic Study and Simulation of Methyl Linoleate Oxidation in Micelles

The kinetics of oxidation (323 K) of bicycloolefins from the norbornene series: norbornene, vinylnorbornene, ethylidenenorbornene, and norbornadiene, inhibited by phenols (PhOH), aromatic amines (AmH), transition metal compounds (Men), or stable nitroxyl radicals of the piperidine series (>NO·), in chlorobenzene solutions have been studied. It has been found that the phenols are single-action inhibitors, whereas the amines, the transition metals, and the nitroxyl radicals repeatedly terminate oxidation chains. The results are explained in terms of phenomenology of the bicycloolefin oxidation process associated with the fact that peroxide radicals attack different reaction centers (π- and α-CH bonds), thereby resulting in the formation of different types of chain carrier radicals: low-molecular-weight hydroperoxide and polyperoxide radicals.

D. V. Loshadkin

Papers

Kinetic Study and Simulation of Methyl Linoleate Oxidation in Micelles

The mechanism of inhibited oxidation of norbornene series bicycloolefins